Clinical case: Tail biting in a pig farm with non-docked pigs

To comply with the European legislation on porcine welfare (2008/120/EC), a multi-site intensive farm with 1200 sows in a 3-week batch farrowing system in Italy decided to stop tail docking to all its animals destined to the production of heavy pigs (slaughter weight of almost 170 kg). The phase where more management problems arose from this decision was the nursery, located in an area separate from the sows and the fatteners. The actual barn has characteristics common to other conventional nurseries, with a plastic slatted floor (according to regulations), pens for almost 60 animals, forced ventilation, and ad libitum dry meal feeding . There are nearly 1800 7-kg piglets in each batch, and the system in place is All-in/All-out. The space per animal is kept within the legal limits, taking into account that the transfer to the growing/finishing barn is done at 30 kg (see Table 1).

Table 1. Summary of available free surfaces for each pig during weaning and growing according to European legislation (2008/120/EC).

The average mortality of the site is close to 3.5%, and the animals are systematically vaccinated against Mycoplasma and PCV2 during lactation. They are then vaccinated against Aujeszky as dictated by the national protocol.

Although the animals already had chains and plastic objects on the ground as environmental enrichment, a new element was added when making the decision to interrupt tail docking: wooden logs attached to a metal chain with plastic discs hanging from the roof in, at least, two points in each pen, so that the maximum number of animals could reach them. The chain and the logs reached the ground so they could be accessible, but no get dirty.

Beginning of tail-biting and consequences on production

Tail biting started at about 15 kg body weight already in the first batch of non-docked animals. The problem persisted and escalated until the animals were transferred to fattening, where it disappeared after a short period of time. At the beginning, a rapid increase of tail lesions was seen, until reaching a prevalence of almost 30% of the animals with serious injuries, with blood and scabs, obvious infections and, in many cases, the loss of a large amount of tissue that implied a reduction in tail length (figure 1).

The distribution of tail biting appeared to be totally random between the different rooms and pens. Very often, one of two adjacent and apparently identical pens within the same room presented the problem with great intensity, and the other one did not. In a first analysis, the production parameters (mortality, weight gain, yield) of weaning were not affected by the episode of tail biting, and only a slight increase in costs related to the antibiotic treatment was detected, inevitably associated with the presence of injuries However, although the problem was completely resolved by transferring the animals from the nursery to the finishing unit, the most obvious losses were recorded in the fattening phase. Specifically, the average mortality in the last fattening phase increased by 2.5% due to the animals that, although the height of tail biting took place several weeks before, exhibited signs of myelitis and ascending infections along the spine, with partially or totally compromised mobility. Both the animals that could not be loaded (due to this reduced mobility) on the lorry destined for the slaughterhouse, and those that did not exhibit apparent signs, had abscesses in the spine that required important parts of the carcasses to be condemned (Figure 2).

Identification of the cause

Tail biting has a multifactorial origin, which prompted the farmer to attribute its origin to a situation of stress, potentially induced by multiple causes. Based on the European Community guidelines of the 2007 EFSA report (The risks associated with tail biting in pigs and possible means to reduce the need for tail docking considering the different housing and husbandry systems), the risk factors present in the farm that could be the main cause of the tail biting were analysed. The five main ones are listed below (you can find the comprehensive list in the 2007 EFSA report).

1. Air and micro-environment quality

Interaction between the onset of tail biting and air and micro-environment parameters is complex, since it also involves factors such as seasonality and climate. However, it can be simplified by highlighting the importance of correct speed and direction of air flow within the barn. In fact, air flows accidentally directed towards the animals, even if they are almost imperceptible (> 0.2 m/s), can increase restlessness. At the same time, however, ventilation must be maintained at a sufficient level to ensure air exchange and oxygenation. In the case farm, a verification of the air flow was carried out with the use of a smoke test, and the noxious gases (CO₂ and ammonia) were quantified, with no disagreements recorded.

2. Competition for resources

Lack of access to resources, especially food, is a very important stressor within a group of animals. If there is not enough space in the feeders, only the largest or dominant animals will have access to them, creating a state of frustration in the subordinates. It is no coincidence that the animals that bite are the smallest of the group, who attack their pen mates in the feeder. Although this was not a risk factor in the farm in question (Table 2).

Table 2. Reference parameters of access to resources (from Managing Pig Health, 2nd edition).

3. Density

It is perhaps one of the most important parameters for the correct prevention of tail biting. It is obvious that the more space the animals have, the lower the risk of tail biting. However, reducing densities has quite important economic impact, since fewer pigs are produced with the same space and the same fixed costs. The density of this farm was kept within the legal boundaries (Table 1). However, a more accurate analysis highlighted that there were frequent delays in the transfer of the animals to the fattening unit, having therefore nearly always animals housed with 0.30 m2/head, even beyond the recommended weight (20-30 kg). Once the problem was identified, the movements in the following batches were planned with greater care.

4. Environmental enrichment

This is such an important aspect that it triggered a second EFSA report in 2016 (Best practices with a view to the prevention of routine tail-docking and the provision of enrichment materials to pigs). Logs with chains are considered unsuitable for pigs because they are only partially edible and do not encourage exploratory behaviour (pigs cannot express their natural rooting behaviour). Therefore it was decided to provide straw inside a metal rack feeder, fixed to the wall or located in the centre of the pen. In order to reduce the risk of blockage of the slats or the pit, and to ensure that the straw that fell to the floor could be manipulated, a carpet was fixed under this straw rack (figure 3).

5. Managing problematic animals

Staff training is essential. It is very important to learn to recognize tail bites as early as possible to isolate the inflicting animal from the rest of the group. This behaviour usually begins with a more nervous animal initiating the aggression . If this animal is immediately stopped, the situation often resolves itself. On the contrary, if the number and severity of the lesions increases, other animals start biting, either because they are attracted to blood in the tails or because they copy their peers' behaviour. Therefore, the members of staff become even more important as regards prevention, and must monitor the pigs with great care. The company has started a continuous training program.

Situation two years down the line

Managing animals with intact tails on a conventional farm is not easy! However, it is not impossible. The inclusion of a correct environmental enrichment and its adequate management —in spite of the slatted floor—, greater care to avoid exceeding the density limits and continuous staff training, allowed to achieve a good balance between productivity and animal welfare, even if these are heavy animals (170 kg)